This invention relates to an optical disc auto-changer for playing a large number of optical discs.
An optical disc is a data storage device on which digital data is written and read optically using a laser. An optical disc is shaped like a phonograph record and is typically made of plastic, metal or glass. Data is written onto the disc coded in binary form by a laser which burns a sequence of tiny craters in the disc along a series of concentric tracks similar to the spiral groove of a phonograph record. The presence or absence of a crater along a track represents a binary one or zero, respectively. Data is read from the disc by directing a laser beam at a track as the disc spins and detecting the presence or absence of such craters by analyzing the reflected beam. The laser-generated craters representing the binary data can be packed so closely together that over a billion bits can be stored on one side of a 12-inch diameter disc. The optical disc has the advantage of storing a large amount of information and maintaining the integrity of that information for a long period of time without the danger of erasure, which exists for magnetic tapes and discs. Magnetic fields or other effects which cause the decay of induced magnetization on a magnetic tape or magnetic disc can obscure the recorded data and cause unintentional erasures. These problems do not affect optical discs. Optical discs are thus ideally suited for permanent files and archival records.
Notwithstanding the large amount of data that can be stored on a single disc, large archival systems still require many discs. Optical disc players are known for holding and playing a single disc. These players require that the disc be inserted manually. Manual operation is undesirable for a large archival system in which a desired disc must be selected quickly from a large bank of discs.
A familiar device for placing one of a large bank of disc-shaped objects on a player is the jukebox for phonograph records. The designs of jukeboxes can be looked to for general guidance on how to construct an auto-changer for optical discs. One such jukebox device is shown in U.S. Pat. No. 3,455,560 to Tuttle. Tuttle discloses a large number of records stored on a circular carousel and a movable arm for grasping one of such records around its edge. The arm then rotates 180.degree. while twisting 90.degree. to place the record on a turntable. The carousel can be rotated so that different records may be accessed.
Another design is shown in U.S. Pat. No. 3,008,721 to Corbett, Jr., et al. Corbett also shows a circular carousel but the turntable is located at the center of the carousel in a vertical position. Records are rolled upward from the carousel onto the turntable where they are played in a vertical position. The record may be rolled from either side of the carousel to play either side of the record. Thus, to turn the record over, it is replaced on the carousel, the carousel is rotated 180.degree. , and the record is again rolled onto the turntable.
The Tuttle and Corbett designs are representative of the problems encountered in extending known jukebox designs to optical disc auto-changers. The rotating and twisting arm of Tuttle must make movements in multiple directions, thereby requiring increased complexity and alignment problems. Complicated mechanisms which increase maintenance requirements are undesirable for optical disc auto-changers where reliability and speed of access are especially important. Proper alignment of an optical disc being placed on a disc player is critical due to the high density of data on an optical disc and the corresponding precision required for reading an optical disc.
The Corbett design requires that the player be mounted vertically, which would add to the complexity and alignment problems for an optical disc player. In addition, optical discs are often used for archival storage of data which is difficult if not impossible to replace if lost, unlike jukebox records, which can normally be readily replaced. Optical discs are often made from glass, and although the data cannot be magnetically erased, optical discs are sensitive to dirt, scratches and smears. Therefore, optical-disc autochangers must be clean and reliable in their operations to avoid damaging the discs. These considerations have impeded attempts to adapt jukebox designs to optical disc auto-changers.